The present invention relates to pressure vessels, and more particularly to pressure vessels of the type comprising a rigid casing having axially aligned ports at its respective ends and a deformable separator dividing the vessel into two variable volume fluid chambers communicating respectively with the port. The deformable separator is in the form of a bladder having a closed lower end and a mouth with a peripheral bead. The bladder is attached at its mouth to an annular supporting member disposed inwardly of and fixed to the casing.